Chapter 15 | Multi-Staining Immunohistochemistry - Dako

Chapter 15 | Multi-Staining Immunohistochemistry
Nanna K. Christensen PhD and Lars Winther PhD
Immunohistochemistry (IHC) has become an established tool for both
research and diagnostic purposes. However, in some cases there is a
need for knowledge about the relative localizations of targets, which
can only be obtained by visualizing all relevant targets in one slide.
this chapter describes the advantages of multi-staining IHC and
various considerations that have to be made to ensure successful
staining. It also discusses the choice of appropriate protocols and
visualization systems.
Advantages of Multiple Staining
Multiple staining can be defined as the detection of two or more targets
on one slide, thus increasing the information obtained from each
slide and reducing turnaround-time compared to single staining or
sequential staining (see definition below). this technique also makes
it possible to assess the topographic relationship of the targets, e.g. to
determine whether targets are present in different cells, in the same
cell or even in the same cellular compartment. In addition, multiple
staining allows the combination of in situ hybridization (ISH) and IHC,
giving information about a particular target both at protein level and
dna/mRna level. Information can also be obtained on possible cellto-cell
spatial contacts of different cell types. Furthermore, with an
increasing demand for less invasive sampling techniques and smaller
and fewer specimens available, multiple staining has an additional
advantage of saving time and reagents.
Examples of Multiple Staining
the diagnosis of prostatic intra-epithelial neoplasia (PIn) is just one
example of the clinical importance of multiple staining. Prostate
needle biopsy is the preferred method for diagnosing early prostate
cancer, but in some cases an ambiguous diagnosis can be made due
to the fact that the biopsy has identified only a few malignant glands
or several histological benign mimics of cancer (1). Since basal cells
are present in the benign cancer mimics, but absent in the malignant
glands, the basal cells can be used to distinguish between the two
cases. Basal cells are labeled using high molecular weight cytokeratin,
cytokeratin 5/6 or p63 immunostaining. In addition, the gene product
of p504s, alpha-methylacyl-Coa-racemase is expressed in a high
percentage of prostate carcinomas, but is negative or only weakly
expressed in benign prostate tissue. thus, it is used as a positive
cancer marker (see example in figure 1). If single-stainings are done
on serial sections, ambiguous lesions may disappear, especially when
dealing with small foci, causing suspected malignancies to remain
undiagnosed. a multiple staining protocol significantly improves
the ability to distinguish between benign and malign lesions. this
reduces the percentage of residual ambiguous lesions and the need
for additional biopsies.
ISH routinely uses multiple staining on slides to determine gene
amplification from the ratio of the signals or from the gene probe of
interest to a reference probe. In addition to the traditional fluorescence
in situ hybridization (FISH), chromogenic versions of the signals in
red and blue colors can also be produced enabling the results to
be evaluated in bright field microscopy. this adds morphological
information to the ratio of signals (Please find additional information
on this subject in Chapter 13, dual-Color CISH).
Technical Challenges
Before embarking on a multi-staining project, some important issues
should be considered:
Since most primary antibodies used today originate from either
mouse or rabbit and are visualized using systems based on antimouse
and anti-rabbit antibodies, the challenge of distinguishing
between primary antibodies has to be addressed. this can require
quite elaborate protocols.
Spectral differentiation of stain colors may be difficult, especially
if the targets are co-localized leading to a mix of colors (2). the
mixed color should be well contrasted with the two basic colors. In
the case where a rare target is co-localized with a more abundant
target one color will tend to dominate the other.
even if targets are not co-localized, it is difficult to balance signals
enabling rare targets to be visible in the same slide as highly
abundant targets. an adjustment in concentration of the primary
antibodies may solve this problem.
If different targets are viewed under different magnifications, it may
be difficult to get the topographic information desired.
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Pre-treatment
Multiple staining, like single staining, can be performed on both
formalin-fixed, paraffin-embedded tissue sections, frozen sections,
cell smears and cytospin preparations. Multiple staining is constrained
by the fact that it may not be possible to find one tissue pre-treatment
protocol that is optimal for all targets. often protocols optimized for
individual stainings differ from one target to the other, e.g. different
target retrieval methods may be used. In this case, it may be necessary
to determine a method that allows all targets to be stained, although
the method may be sub-optimal for some targets.
In cases where targets of different abundance are to be stained, a
method must be selected to best balance the signals. Combining
ISH and IHC on one slide is particularly challenging because targets
require very different pre-treatment protocols. Since ISH processes
such as dna denaturing are not compatible with the presence of the
antibodies for IHC, the ISH protocol is normally performed first.
Multi-Staining Method Selection
to ensure success, IHC staining must be carefully planned. this is
even more important with multi–staining. If primary antibodies, both
directly-labeled and unlabeled and from different host-species, are
commercially available, there are several different staining methods
that one can choose. However, very often the choice may be limited
by the reagents available (3). Care must be taken to avoid crossreactivity
between reagents. a flow chart or similar aid might prove
useful in selecting the best method.
In general, staining methods can be divided into the following classes:
Sequential staining: By this method, one staining procedure
succeeds another. For example, the first primary antibody is applied
to the tissue section followed by a labeled detection system such as
streptavidin-biotin horseradish peroxidase (HRP), with a chromogen
such as daB. the second primary antibody is applied only after the
excess daB is rinsed off, followed by labeling with a streptavidinbiotin
alkaline phosphatase (aP) detection system and a colored
chromogen. the biggest advantage of sequential staining is that by
this procedure problems related to cross-reactivity are avoided.
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a sequential staining is shown in Figure 1. Here, the primary and
secondary antibodies from the first staining were eluted before the
staining of the next target was performed. the disadvantages of
sequential staining are: the method cannot be used for co-localized
targets, the technique often leads to a long staining protocol
and carries an inherent risk of incorrect double staining due to
insufficient elution of one set of reagents before application of the
next reagent.
Figure 1. Sequential double staining method performed with the EnVision TM G⎜2
Doublestain Kit using polyclonal anti-kappa light chains (red) and polyclonal
anti-lambda light chains (brown) as primary antibodies. Formalin-fixed, paraffinembedded
tissue sections from tonsils.
elution may become an issue with some high-affinity primary
antibodies as these may remain at their binding site, leading to
spurious double stained structures. elution also risks denaturing
epitopes of antigens to be visualized subsequently. Furthermore, for
some chromogens there is a risk that the first chromogen (daB in
particular) may shield other targets. this technique is, therefore, not
recommended for evaluation of mixed colors at sites of co-localization,
because not all reaction products are capable of surviving the rigorous
washing required to remove the antibodies. to avoid such problems
and blurry staining results, it is recommended to use the most “robust”
dyes such as daB, Fast Red, aeC and X-gal first followed by other
less “robust” dyes.

Simultaneous staining: In a simultaneous double stain, the primary
antibodies can be applied simultaneously. the advantage of this
method is that it is less time-consuming because the reagents can be
mixed together. However, the technique can only be used, if suitable
primary antibodies are available. two methods can be adopted: a
direct method with directly-labeled primary antibodies, or an indirect
method based on unlabeled primary antibodies raised in different host
species, or of different Ig isotype or Igg subclass (4).
a simple example of the direct method is when the primary antibodies
are fluorescence-labeled to allow direct visualization. this avoids
cross-reactivity, but is rarely practical since some form of amplification
is necessary to get sufficient signal. alternatively, the primary
antibodies may be conjugated directly with enzymes, biotin, haptens or
fluorochromes, subsequently employing the corresponding secondary
antibody or streptavidin reagent. this is less time-consuming than the
sequential method, since primary and secondary antibodies can be
mixed together in two incubation steps. However, it requires avoiding
all cross-reactivity.
With the indirect method it is also possible to apply time-saving
antibody cocktails since the primary antibodies are recognized
by different secondary antibodies (for an example, see Figure 2).
generally, it is advantageous to use secondary antibodies raised
in the same host in order to prevent any unexpected interspecies
cross-reactivity. one example of such a system is the new enVision
duoFLeX from dako. this system applies a mixture of primary
antibodies of mouse and rabbit origin, followed by a mixture of the
secondary goat-anti mouse and goat-anti-rabbit antibodies labeled
with HRP and aP, respectively. Finally, the chromogens are applied
sequentially. the result is a double stain where the primary mouse
antibodies are stained brown with daB and the primary rabbit
antibodies are stained red with Permanent Red (for an example,
see Figure 2). the system has been developed for dako’s new line
of RtU cocktails of primary antibodies, but may also be used with
other antibody cocktails or individual antibodies that are sequentially
incubated on a single slide.
Multi-Staining Immunohistochemistry
Figure 2. Simultaneous double staining performed with EnVision TM DuoFLEX
using an antibody cocktail containing monoclonal rabbit anti-AMACR (red),
monoclonal mouse anti-HMWCK and monoclonal mouse anti-CK 5/6 (brown/
black). Formalin-fixed, paraffin-embedded tissue sections from prostate.
Multi-step technique (3): this is an indirect/direct method combining
unlabeled primary antibodies with directly-conjugated antibodies.
the method starts with staining the unlabeled antibody/antibodies
with the appropriate detection system, but without performing the
final enzymatic staining reaction. the tissue is blocked with normal
serum from the host of the first primary antibody before the second,
directly-labeled primary antibody is added. the staining ends with the
two enzymatic reactions being performed sequentially.
Multi-step staining can be used when the selection of primary
antibodies is limited. However, when using this method it is not
possible to mix reagents.
Users will often find that the choice of staining method is limited
by the availability of the primary antibodies with respect to species
origin or label.
difficulties arise when targets are known or suspected to be
co-localized and the only available primary antibodies are unlabeled
monoclonal mouse antibodies of the same Igg subclass. In that case,
none of the techniques described above are applicable.
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one solution is the dako animal Research Kit (aRK ), which contains
reagents for labeling mouse primary antibodies with a biotinylated
anti-mouse Fab fragment, followed by blocking of the remaining
reagent with normal mouse serum. this can be applied to the tissue
as part of the multi-step technique (5). the kit gives a non-covalently
labeled antibody, thus avoiding the risk of reducing the affinity. In
addition, only small amounts of primary antibody are needed and the
kit does not require time-consuming purification steps.
another solution is Zenon technology (Invitrogen) developed for flow
cytometry. It essentially uses the same technique and offers labeling
kits for mouse primary antibodies available as enzyme conjugates or
conjugated to one of a wide variety of fluorescent dyes.
Finally, it is important to be aware of the fact that visualization systems
with dual recognition such as the enVision + dual Link System do not
discriminate between species, and thus are only suitable for multiple
staining when using the sequential method. Visualization kits with
amplification layers that are not well specified should be avoided since
possible cross-reactivity cannot be predicted.
Selection of Dyes
the primary choice to make when deciding how to make the targets
visible is whether to use immunoenzyme staining or fluorescence.
Both have advantages and disadvantages and in the end, decisions
should be made based on conditions of the individual experiment.
Chromogenic Dyes
examples of enzyme/chromogen pairs suitable for triple staining are:
gal/X-gal/turquoise, aP/Fast blue, HRP/aeC/Red
HRP/daP/Brown, gal/X-gal/turquoise, aP/Fast red
HRP/daP/Brown, aP/new Fucsin/Red, HRP/tMB/green
When selecting color combinations for multiple staining with
chromogenic dyes, it is advisable to choose opposing colors in
the color spectrum such as red and green to facilitate spectral
differentiation. If using a counterstain, this must also be included
in the considerations. When working with co-localized targets,
dyes must be chosen so that it is possible to distinguish the mixed
color from the individual colors. double staining using chromogenic
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dyes is well-established, but if the targets are co-localized, the
percentage of the single colors cannot be easily identified (6). For a
triple staining, it is naturally more difficult to choose colors that can
be unambiguously differentiated and even more so, if targets are
co-localized. In such cases, a technique known as spectral imaging
may be applied (2). Spectral imaging allows images of the single
stains to be scanned and by using specialized software algorithms
the colors are unmixed displaying the distribution and abundance of
the individual chromogens.
Visualizing Rare Targets
a narrow, dynamic range is a disadvantage for immunoenzymatic
staining. the precipitation process, which is crucial for this method,
is only triggered at a certain concentration of substrate and product.
on the other hand, at high concentrations the precipitated product
may inhibit further reaction. therefore, it is difficult to visualize rare
targets and highly abundant targets in the same slide. to ease this
problem, catalyzed signal amplification — an extremely sensitive
IHC staining procedure (such as e.g. CSa from dako) can be used.
the method can bring rare targets within the same dynamic range
as highly expressed targets.
Fluorescent Dyes
double immunofluorescence labeling is quite well established (7). Some
of the same considerations as with chromogenic dyes apply when
working with immunofluorescence. It is equally necessary to select
dyes with distinguishable spectral properties. However, there are more
colors available and the emissions spectra of the fluorescent molecules
are narrower than the spectra of the chromogenic dyes. the use of
multiple-fluorescent colors is also well established in FISH and flow
cytometry, where dichroic and excitation/emission filters are employed
to separate different fluorescent signals. the spectral separation can
be aided by digital compensation for overlapping emission spectra.
In addition, new fluorescent microscope systems such as e.g. Laser
Scanning Confocal Microscope can unmix the spectral signatures of
up to eight fluorochromes without any problems using multi-spectral
imaging techniques such as e.g. emission fingerprinting (8).

When staining targets that are co-localized, fluorescent dyes allow
separate identification of targets. this makes it possible to discern
targets even in very different concentrations, whereas subtly mixed
colors from chromogenic dyes may easily pass unnoticed with
immunoenzyme staining.
Immunofluorescence potentially has a wider, dynamic range than
immunoenzyme staining (9). Using this method, there is no enzymatic
amplification involved and thus the dynamic range is determined
solely by the sensitivity of the detectors.
on the other hand, there are some inherent problems with the use of
immunofluorescence or fluorescence in general:
a fluorescent signal is quenched when the fluorochromes are in
close proximity (10)
dyes undergo photobleaching when subjected to light and will thus
only fluoresce for a limited time.
even when stored away from light, fluorochromes will slowly
deteriorate at room temperature.
the morphology viewed in slides is different from what is observed
in an immunoenzyme staining with counterstains.
Increased background staining due to autofluorescence can pose
a problem when working with some formalin-fixed tissues.
In spite of these drawbacks, immunofluorescence gives clear, sharp
localization of targets and has advantages over chromogenic dyes
when working with co-localized targets. Some chromogenic dyes
fluoresce as well, such as e.g. Fast Red — an aP-substrate which is
brighter in fluorescence microscopy than in bright field microscopy.
(for a detailed review of the immunofluorescence technique, see
Chapter 11, Immunofluorescence).
alternatives to the conventional chromogenic dyes are colloidal, gold-
labeled antibodies that can be used with normal light microscopy
with silver-enhancement, green Fluorescent Proteins (gFP and
their variants) and Quantum dots. the latter, especially, has been
found to be superior to traditional organic dyes on several counts
such as brightness (owing to the high-quantum yield) as well as their
higher stability (owing to less photodestruction). they can be linked
to antibodies or streptavidin as an alternative to fluorochromes (11, 12).
Multi-Staining Immunohistochemistry
However, the size of these conjugates pose diffusion problems in
terms of getting these inorganic particles into cells or organelles.
Automated Image Acquisition and Analysis
in Multiple Staining
digital image analysis will increase the number of usable dyes since
it does not rely on the human eye for detection and differentiation. a
digital image is acquired at excitation wavelengths relevant for the
dyes applied, and separate detectors record individual colors. thus,
digital image analysis e.g. will allow the combination of fluorescent
and immunoenzyme dyes.
detectors, however, have biased color vision. they amplify colors
differently than does the human eye. therefore, dyes used in
image analysis should be optimized for the best fit possible with the
detector’s filter properties.
Image analysis systems contain algorithms that allow compensation
for overlapping emission spectra comparable to flow cytometry. they
also allow signal gating within an interesting range of wavelengths,
enabling users to see only signals within the desired range. Visualizing
a combination of several gates with color selected independently of
the dyes used for staining may clarify pictures and make conclusions
easier to reach. this also makes it possible to determine signal
intensity to exclude unspecific staining or background staining from
final images.
another advantage of digital image analysis is that it allows signal
quantitation. through software algorithms users can count how many
signal clusters exceed a certain level of intensity and, potentially,
calculate the ratio of different cell types. e.g. an image analysis
algorithm can calculate the percentage of cells that stain positive
for a certain target, combine that percentage with information of
another stained target and, based on this, highlight diagnosis. a more
thorough discussion of image acquisition and analysis can be found
in Chapter 18, Virtual Microscopy and Image analysis.
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Conclusion
Multiple-target staining will one day be a routine procedure just as
single-target staining is today. Use of the technique will extend, since
it offers reduced turnaround-time and information not obtainable
from single-target staining. availability of reagents that give a wider
range of possibilities when it comes to choice of technique, such as
e.g. labeled primary antibodies and antibodies raised in different
host species, will likely increase. In addition, some suppliers now
offer complete kits with clinically-relevant antibody cocktails and
visualization systems optimized to give the correct, balanced stain,
thus significantly reducing the workload for the user.
Software for automated image acquisition and analysis will play
a key role in this evolution since the limit to how many colors the
human eye is capable of distinguishing is limited. analysis algorithms
will never entirely replace a skilled pathologist, but algorithms will
gradually improve as the amount of information loaded into underlying
databases increase. eventually, algorithms will become sufficiently
“experienced” to be able in many cases to suggest a diagnosis, and
only the final decision will be left for the pathologist.
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References
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2. Van der Loos CM, J Histochem Cytochem 2008; 56:313-28.
3. Van der Loos CM. Immunoenzyme Multiple Staining Methods, BIoS
Scientific Publishers Ltd. 1999.
4. Chaubert P et al. Modern Pathology 1997; 10:585-91.
5. Van der Loos CM and göbel H J Histochem Cytochem 2000; 48:1431-7.
6. Merryn V.e. Macville analytical Cellular Pathology 2001; 22: 133-42.
7. Mason d Y et al. J Pathol 2000; 191:452-61.
8. dickinson Me et al. Bio techniques 2001; 31: 1272-8.
9. Landon a. et al. the Journal of Pathology, 2003, 200: 577-88(12).
10. Förster th., Fluoreszenz organischer verbindungen, Vandenhoeck &
Ruprecht, 1951.
11. Wu X et al. nat Biotechnol 2003; 21:41-6.
12. the small, small world of quantum dots. CaP today.december 2008.